The present invention relates to stepper control systems. In particular, the present invention relates to stepper motor control systems in which a digital processor, such as a microprocessor, controls the speed of a stepper motor as a function of numbers stored in look-up tables.
A stepper motor is a motor which rotates or drives in incremental steps. The rate of rotation or speed of the stepper motor is determined by the frequency of drive signals to the stepper motor. Since the stepper motor is essentially digital in nature, it is particularly well suited for use with digital electronic systems. In addition, it provides highly accurate drive distances with the tolerance being determined by the incremental rotation produced by one stepper motor step. Stepper motors have found application, for example, in photographic paper cutters and film cutters, where highly accurate drive distances are required.
In many stepper motor systems, it is desirable to provide stepper motor drive signals which have an exponentially increasing frequency to the desired maximum drive frequency in order to accelerate the stepper motor. Similarly, an exponentially decreasing frequency from the maximum drive frequency is desirable in order to decelerate the stepper motor prior to stopping. In the past, devices which provide up and down ramp frequency signals for stepper motors have generally been analog in nature. As a result, they have been generally complex and relatively inaccurate.
In U.S. Pat. No. 4,042,973 by P. J. Caulfield et al, a closed loop feedback digital system is described which generates a square wave type signal of exponentially varying frequency. This system may be used to provide the up ramp (i.e. acceleration) and down ramp (i.e. deceleration) signals for a stepper motor. This system, however, is relatively specialized and limited in the frequency variations which can be produced. A system having greater flexibility is desirable.